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| Titel |
Assessment of Halon-1301 as a groundwater age tracer |
| VerfasserIn |
M. Beyer, R. van der Raaij, U. Morgenstern, B. Jackson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 19, no. 6 ; Nr. 19, no. 6 (2015-06-17), S.2775-2789 |
| Datensatznummer |
250120742
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| Publikation (Nr.) |
 copernicus.org/hess-19-2775-2015.pdf |
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| Zusammenfassung |
Groundwater dating is an important tool to assess groundwater resources in
regards to their dynamics, i.e. direction and timescale of groundwater flow
and recharge, contamination risks and manage remediation. To infer
groundwater age information, a combination of different environmental
tracers, such as tritium and SF6, are commonly used. However, ambiguous
age interpretations are often faced, due to a limited set of available
tracers and their individual restricted application ranges. For more robust
groundwater dating multiple tracers need to be applied complementarily (or
other characterisation methods need to be used to complement tracer
information). It is important that additional, groundwater age tracers are
found to ensure robust groundwater dating in future.
We have recently suggested that Halon-1301, a water soluble and entirely
anthropogenic gaseous substance, may be a promising candidate, but its
behaviour in water and suitability as a groundwater age tracer had not yet
been assessed in detail. In this study, we determined Halon-1301 and
inferred age information in 17 New Zealand groundwater samples and various
modern (river) water samples. The samples were simultaneously analysed for
Halon-1301 and SF6, which allowed for identification of issues such as
contamination of the water with modern air during sampling. All analysed
groundwater sites had also been previously dated with tritium, CFC-12,
CFC-11 and SF6, and exhibited mean residence times ranging from modern
(close to 0 years) to over 100 years. The investigated groundwater samples
ranged from oxic to highly anoxic. All samples with available CFC data were
degraded and/or contaminated in one or both of CFC-11 and CFC-12. This
allowed us to make a first attempt of assessing the conservativeness of
Halon-1301 in water, in terms of presence of local sources and its
sensitivity towards degradation, which could affect the suitability of
Halon-1301 as groundwater age tracer.
Overall we found Halon-1301 reliably inferred the mean residence time of
groundwater recharged between 1980 and 2014. Where direct age comparison
could be made 71% of mean age estimates for the studied groundwater sites
were in agreement with ages inferred from tritium and SF6 (within an
uncertainty of 1 standard deviation). The remaining (anoxic) sites showed
reduced concentrations of Halon-1301 along with even further reduced
concentrations of CFCs. The reason(s) for this need to be further assessed,
but are likely to be caused by sorption or degradation of the compounds.
Despite some groundwater samples showing evidence of contamination from
industrial or agricultural sources (inferred by elevated CFC
concentrations), no sample showed a significantly elevated concentration of
Halon-1301, which suggests no local anthropogenic or geologic sources of
Halon-1301 contamination. |
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